with beersmith you can sync desktop apps using dropbox but when it comes to mobile apps, all dropbox does is give a listing of the files available in your dropbox. you have to choose a file to download to your phone, it's not automatic. for me I use Brewzor Pro on android and import my recipes via BeerXML files from beersmith.
While it seems like a good idea to have the mobile app and desktop app auto sync the programming of it would be a nightmare. Then add in which mobile platform? IOS handles everything different from Android. Then you have to decide which to do first. Right now, Android is the most popular mobile OS out there, a year ago that wasn't the case. If they were to pick Android first, the iPhone crowd would get pissed. If the did iPhone first, Android crowd gets pissed. If anything they'd write a version for Win7 phone since it would be easier to port it over, but that pisses off both iPhone and Android users.
For now, I wouldn't hold your breath waiting for a mobile beersmith app and just be happy with the apps we have available right now.